• Title/Summary/Keyword: 회전 레이놀즈수

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Cooling of a Rotating Heated Flat Plate by Water Jet Impingement (회전전열평판(回轉傳熱平板)의 충돌수분류(衝突水噴流)에 의한 냉각(冷却))

  • Jeon, Sung-Taek;Kim, Yeun-Young;Lee, Jong-Su;Park, Jong-Suen;Lee, Doug-Bong
    • Solar Energy
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    • v.15 no.2
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    • pp.47-64
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    • 1995
  • An experimental investigation is carried out to see the local heat transfer characteristics of a rotating heated flat plate surface with constant heat flux when a normal water jet is impinging on this surface. The effects of jet Reynolds number, rotating Reynolds number are investigated while the distance between the nozzle and the flat plate is set fixed. As a result, correlations to relate the local Nusselt number to the local rotational Reynolds number, jet Prandtl number and the dimensionless radial position are presented.

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Performance Analysis of Autorotation(1) : Analysis Method and the Effect of Aerodynamic table (자동회전의 성능해석(1) : 해석 기법과 공력 테이블의 영향)

  • Kim, Hak-Yoon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.40 no.1
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    • pp.1-11
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    • 2012
  • Performance analysis was performed for an autorotating rotor. For a given airspeed, shaft angle, and collective pitch, the steady state of autorotation was judged by using the transient simulation method(TSM), then the thrust, lift, and drag coefficient for that state were computed. Average thrust was calculated from the instantaneous thrusts, in which the TSM was used in blade thrust integration. The analysis method was applied to the model rotor that had been tested by wind tunnel. Some comparison between analysis and test was provided. Two types of two-dimensional airfoil aerodynamic data were utilized in analysis, and they were made by Navier-Stokes Solver in terms of Reynolds and Reynolds-Mach number. The quantitative difference of results using two data set was examined and compared.

An Experimental Study on the Transitional Flows in a Concentric Annu- lus with Rotating Inner Cylinder (안쪽축이 회전하는 환형관내 천이유동에 관한 연구)

  • 김영주;김철수;황영규
    • Journal of Energy Engineering
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    • v.11 no.4
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    • pp.299-305
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    • 2002
  • The present experimental and numerical investigations are performed on the characteristics of transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully devel-oped flow of water and that of 0.2% CMC-water solution at a inner cylinder rotational speed of 0∼600 rpm, respectively. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, it is gradually decreased for turbulent flow regime.

Aerodynamic Design and Performance Analysis of a Propeller at Low Reynolds Number Flow Conditions (저 레이놀즈수 유동조건에서의 프로펠러 공력설계 및 성능해석)

  • Yun, Senghyun;Han, Cheolheui
    • Journal of Aerospace System Engineering
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    • v.9 no.1
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    • pp.7-11
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    • 2015
  • 최근 무인기와 초소형비행체를 위한 프로펠러 연구수요가 증가하고 있다. 일반적인 프로펠러와 다른 점은 저 레이놀즈수 유동조건에서 구동된다는 점이다. 본 연구는 저 레이놀즈수 유동조건에서 비행하는 인간 동력 항공기를 위한 프로펠러 공력설계 및 성능해석에 관한 연구다. 저 레이놀즈수 유동조건에서 발생하는 공력천이현상을 고려한 3차원 공력특성 변화를 정확히 반영하지 못하는 상용 프로그램의 단점을 보완하여 프로펠러 공력설계 및 성능해석이 가능한 프로그램을 개발했다. 개발된 프로그램으로 인간 동력 항공기 설계요구조건에 충족하는 프로펠러 공력설계 및 성능해석을 수행하였다. 또한 프로펠러 회전수와 장착각도 변화에 따른 성능변화를 예측하여 비행당시 상황에 따라 비행 가능한 성능출력이 가능하도록 하였다.

Heat transfer characteristics between a rotating flat plate and an impinging water jet (회전전열평판과 충돌수분류간의 열전달특성에 관한 실험적 연구)

  • 전성택;이종수;최국광
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.10 no.5
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    • pp.509-522
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    • 1998
  • An experimental investigation is reported on the heat transfer coefficient from a rotating flat plate in a round turbulent normally impinging water jet. Tests were conducted over a range of jet flow rates, rotational speeds, jet radial posetions with various combinations of three jet nozzle diameter. Dimensionless correlation of average Nusselt number for laminar and turbulent flow is given in terms of jet and rotational Reynolds numbers, dimensionless jet radial position. We suggested various effective promotion methods according to heat transfer characteristics and aspects. The data presented herein will serve as a first step toward providing the information necessary to optimize in rational manner the cooling requirement of impingement cooled rotating machine components.

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Flow of Non-Newtonian Fluids in an Annulus with Rotation of the Inner Cylinder (안쪽축이 회전하는 환형관내 비뉴튼유체 유동 연구)

  • 김영주;우남섭;황영규
    • Tunnel and Underground Space
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    • v.12 no.4
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    • pp.277-283
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    • 2002
  • This experimental study concerns the characteristics of a helical flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. The pressure losses and skin friction coefficients have been measured for the fully developed flow of Non-Newtonian fluid, aqueous solution of sodium carbomethyl cellulose (CMC) and bentonite with inner cylinder rotational speed of 0~400 prm. Also, the visualization of helical flows has been performed to observe the unstable waves. The results of present study reveal the relation of the Reynolds number Re and Rossby number Ro with respect to the skin friction coefficients. In somehow, they show the existence of flow instability mechanism. The pressure losses increase as the rotational speed increases, but the gradient of pressure losses decreases as the Reynolds number increases in the regime of transition and turbulence. And the increase of flow disturbance by Taylor vortex in a concentric annulus with rotating inner cylinder results in the decrease of the critical Reynolds number with the increase of skin friction coefficient.

Measurement of Reynolds Number Effects on Cavitation Performance in a Turbopump Inducer (레이놀즈 수가 터보펌프 인듀서 캐비테이션 성능에 미치는 영향 측정)

  • Kim, Junho;Song, Seung Jin
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2017.05a
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    • pp.820-823
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    • 2017
  • This study experimentally investigate how the Reynolds number affect cavitation performance in a turbopump inducer using water. Cavitation performance has been determined by the static pressure measured at the inlet of the inducer. Reynolds number has been varied by varying water temperature and inducer rotational speed to maintain constant non-dimensional thermal parameter. At low non-dimensional thermal parameter, the critical cavitation number is insensitive to Reynolds number. However, at high non-dimensional thermal parameter, the critical cavitation number increased as Reynolds number increases. Thus, cavitation performance is deteriorated as Reynolds number increases when thermal effect exists.

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The Aerodynamic Origin of Abrupt Thrust Generation in Insect Flight (Part 2: Study on Primary Aerodynamic Parameters) (곤충비행에서 갑작스러운 추력발생의 공기 역학적 원인 Part 2: 공기역학적 주요 변수에 대한 연구)

  • Lee, Jung-Sang;Kim, Jin-Ho;Kim, Chong-Am
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.35 no.1
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    • pp.10-17
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    • 2007
  • Numerical results from the "figure-of-eight" motion of Phormia-Regina in Part 1 indicate that vortical structure and vortex dynamics do play a critical role in lift and thrust generation. The aerodynamic force generation of insects' wing could be governed by aerodynamic parameters such as Reynolds number; kinematic parameters such as frequency, amplitude, and component of the figure of eight motion; and morphological parameters such as wing shape and the number of wing. In the present work, the effects of Reynolds number, reduced frequency and motion component are investigated in detail to clarify aerodynamic characteristics of insect wing. Through numerical results and their physical interpretation, the mechanism of aerodynamic force generation is presented more clearly. Rotation turns out to be the most important component in thrust generation and subsequent counterclockwise rotational circulation is closely related with thrust generation.

An Unsteady Numerical Method of Autorotation and the Effect of 2D Aerodynamic Coefficients (자동회전의 비정상 수치해법과 2차원 공력계수의 영향)

  • Kim, Hak-Yoon;Sheen, Dong-Jin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.2
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    • pp.121-130
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    • 2009
  • An unsteady numerical simulation method for an autorotating rotor in forward flight was developed. The flapping and rotational equations of motion of autorotation are continuously integrated for given time steps, meanwhile the induced velocity field at disc plane is obtained by the dynamic inflow theory embodying the unteadiness. The transitions from arbitrary initial states to equilibrium states were simulated. Steady autorotations as numerical solutions of equations were predicted by using two sources of blade airfoil data. The simulations using airfoil data which were obtained by a two dimensional Navier-Stokes solver in terms of angles of attack and Reynolds numbers have shown good agreements with wind tunnel experimental results.

Experimental Study for the Influence of Rotator Shape on the Rotating Flow in a Confined Cylinder (밀폐된 원통내부에서 회전체의 형상이 회전유동에 미치는 영향에 관한 실험적 연구)

  • Kim, Yu-Gon;Park, Cheon-Su
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.5
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    • pp.675-684
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    • 2002
  • Two-dimensional, angle-resolved LDV(Laser Doppler Velocimetry) measurements of the turbulent rotating flow field in a confined cylinder have been performed. The configurations of interest are flows between a rotating upper disk with a rod attached by a disk or impeller($\theta$ = 45$^{\circ}$, 90$^{\circ}$) and a stationary lower disk in a confined cylinder. The mean flow velocity as well as the turbulent intensity of the flow field have been measured. The results show that the flow is strongly dependent on the position of the impellers or the disk, negligibly affected by the Reynolds number in turbulent flow. It is observed that the mixing effect of the axial flow impeller($\theta$ = 45$^{\circ}$) is better than that of the radial flow impeller($\theta$ = 90$^{\circ}$) or a disk.